This invention relates to an outboard motor and more particularly to an exhaust arrangement for outboard motors.
As is well known, the design of the exhaust system for an outboard motor is an area that presents considerable problems. The reason for this is that the space available for treating and silencing the exhaust gases before discharge to the atmosphere is quite small. For that reason, it has been the practice to discharge the exhaust gases under most running conditions through an underwater exhaust gas discharge. Thus, the body of water in which the watercraft is operating may be utilized as a silencing medium.
In addition to this, the problem of discharging cooling water from the engine when the engine is of the water-cooled type, as is typical with most outboard motors. In an outboard motor, the engine cooling system relies on water from the body of water in which the watercraft is operating. This water is circulated through the engine and then returned back to the body of water in which the watercraft is operated. In this way, the body of water actually acts as a heat exchanger for the engine cooling which provides significant improvement.
It has been the practice to utilize an arrangement wherein the cooling water is returned along with the exhaust gases to the body of water. If this is done in a proper way, the water that has been drawn from within the body of water in which the watercraft is operating can also be utilized to cool the exhaust gases and provide some silencing.
However, since most outboard motors use two-cycle engines, there are some particular dangers in doing this. With two-cycle engines, there is frequently a negative pulse in the exhaust system during a normal operating cycle. Thus, if the cooling water is discharged in proximity to the exhaust system, it may actually be drawn into the combustion chamber during this negative pulse condition. Obviously, this is not desirable.
It is, therefore, a principal object of this invention to provide an improved exhaust system for an outboard motor.
It is a further object of this invention to provide an exhaust system for an outboard motor wherein the coolant for the engine can also be employed to cool the exhaust system.
It is a further object of the invention to provide an exhaust system cooling arrangement for an outboard motor as described, wherein the cooling water is returned in such a way that it will not come into direct contact with the exhaust gases and thus cannot be drawn back into the engine.
Frequently, the drive shaft housing of the outboard motor is employed in some manner as an expansion chamber. This expansion chamber cooperates with an exhaust pipe that delivers the exhaust gases from the engine into the expansion chamber, and which functions to assist in the silencing of the exhaust gases before they are discharged into the water. Frequently, the cooling water from the engine is also discharged into this expansion chamber and thus this gives rise to the possibility of water injection through the exhaust system, as before referred to.
It is a further object of this invention to provide an improved outboard motor exhaust system employing an expansion chamber in the drive shaft housing and in which the exhaust gases and water can be mixed in such a way that the water is not directed toward the exhaust pipe.